A hybrid drive train of a motor vehicle with a parallel operating arrangement of an internal combustion engine and an electric motor can be, in connection with a manual transmission arranged downstream in terms of drive technology, constructed in such a geometrically simple way, that the electric motor is arranged coaxially on the input shaft of the transmission. The electric motor is rotationally fixed to the input shaft of the transmission, and the driveshaft of the internal combustion engine can be connected to the input shaft of the transmission via a controllable decoupler, that can be engaged and disengaged.
In this case, the electric motor can be selectively shifted without power during driving operation, for use as a generator to charge an electrical energy store, or for use as an electric motor for driving the motor vehicle. During motor operation, the electric motor, with an engaged decoupler, particularly during rapid acceleration and when driving up a steep incline, can be used to support the internal combustion engine in so-called boost operation, and with a disengaged decoupler, particularly starting and when driving in inner-city areas with limits on emissions, the electric motor can be used as the only drive motor in purely electrical operation.
However, one disadvantage of this kind of hybrid drive train is that the engine-speed level of the electric motor is identical to that of the internal combustion engine, and the electric motor must therefore be constructed as relatively large and heavy in order to achieve adequate output in the electrically powered mode. However, in connection with an axially parallel arrangement of the electric motor and a drive connection of the rotor of the electric motor to the input shaft of the transmission by means of an input stage with a high ratio, such as a pair of spur gears or a continuously variable transmission, the electric motor can be designed to have lower output and be smaller in size. However, a significant disadvantage of this hybrid drive train is the interruption in the flow of force during shifting operations, which results in poor driving performance and less comfort.
Various forms of construction of hybrid drive trains have therefore been proposed, in which the electric motor, in terms of drive technology, is integrated by means of a differential transmission with three drive elements, whereby the first drive element has a drive connection with an input shaft of the transmission that can be connected to the internal combustion engine by means of a decoupler, the second drive element has a drive connection with the rotor of the electric motor, and the third drive element has a drive connection with an additional transmission shaft of the gearshift, for example the output shaft or a second input shaft.
A first hybrid drive train of this type is described in DE 198 49 156 A1, with regard to the embodiment of the to Claims and FIG. 2 in particular. The transmission in question features an input shaft and an output shaft which can be selectively connected in each case with assigned gearwheel sets of different gear ratios by means of an assigned clutch. The driveshaft of the internal combustion engine can be connected by means of a controllable decoupler to the input shaft of the transmission. The electric motor is arranged coaxially in a contact-free manner about the input shaft of the transmission. The differential transmission is designed as a simple planetary gearset with a sun gear, a planet carrier that carries a plurality of planetary gears whose gear teeth engage the sun gear, and a ring gear whose gear teeth engage one of the planet gears, which is also arranged coaxially about the input shaft of the transmission. The planet carrier forms the first drive element of the differential transmission and is rotationally fixed with the input shaft of the transmission. The sun gear forms the second drive element of the differential transmission and is rotationally fixed with the rotor of the electric motor. The ring gear forms the third element of the differential transmission and has a drive connection to the output shaft of the transmission by means of decoupling stage comprised of a pair of spur gears.
The differential transmission forms a parallel power branch to the gearshift, whereby the percentage or the magnitude of the power transmission of the differential transmission can be regulated by activation of the electric motor. During a shifting operation, it is provided that the torque of the internal combustion engine is more or less completely transmitted through the differential transmission before the engaged gear under load is disengaged, the target gear is synchronized, and then the next gear engaged. Then the electric motor is shifted without power and, in this way, the torque of the internal combustion engine is again completely transmitted via the gearshift to the output shaft.
However, because the synchronization of the target gear is suppose to take place via the relatively sluggish engine control, there are long response times and a correspondingly high electric output of the electric motor in order to support the torque that is transmitted. In order to enable the supporting function, the electric motor must be designed for at least the maximum torque of the internal combustion engine, reduced by the effective ratio, because otherwise torque interruptions could occur during the shifting operations. During normal driving operation, i.e., with an engaged decoupler and a gear engaged in the transmission, the electric motor can be used as a generator for charging an electric energy storage or as an engine to support the internal combustion engine. When the transmission is in neutral, and the output shaft is blocked, and the internal combustion engine can be started using the electric motor. When the transmission is in neutral, with an engaged or a missing decoupler, and a running internal combustion engine, starting can take place using the electric motor by means of a continuous increase of the support torque, at least until synchronous operation of the clutch of the first gear is reached, and the clutch can be engaged. Purely electric drive operation, with the electric motor as the only drive engine, is possible with a disengaged decoupler and with an engaged gear in the gearshift, but even with an engaged first gear, particularly in order to start the vehicle, this would produce an unfavorably low overall gear ratio of the electric motor compared to the output shaft.
An additional hybrid drive train of this type is known from EP 0 845 618 B1. The transmission described here features two coaxially arranged input shafts that can be selectively connected, in each case by means of an assigned clutch, with the output shaft using alternately assigned gearwheel sets of different ratios. The driveshaft of the internal combustion engine can be, in each case, connected to the two input shafts by means of a controllable decoupler. The electric motor is arranged axially parallel to the two input shafts. The differential transmission is designed as a simple planetary gearset with a sun gear, a planet carrier that carries a plurality of planet gears whose teeth engage the sun gear, and a ring gear whose gear teeth engage the planet gears, and the electric motor is arranged about the first input shaft. The planet carrier forms a first drive element of the differential transmission and is rotationally fixed to the first input shaft of the gearshift. The sun gear forms a second drive element of the differential transmission and has a drive connection to the rotor of the electric motor by means of an input constant consisting of two gearwheels. The ring gear forms a third drive element of the differential transmission and is rotationally fixed to the second input wheel.
During normal drive operation, one decoupler is engaged and a gear assigned to the respective input shaft is engaged. The other decoupler can also be engaged, in which case the differential transmission revolves in a fixed manner. In this operating state, all of the gears assigned to the input shaft in question must be disengaged, otherwise the gearshift would be locked. The rotational speed of the rotor of the electric motor corresponds to the multiplication of the rotational speed of the internal combustion engine determined by the ratio of the input constants. During this phase of operation, the electric motor can be used as a generator for charging an electrical energy storage facility or as an engine to support the internal combustion engine.
During a shifting operation from a gear under load assigned to an input shaft to a target gear assigned to the other input shaft, it is provided that the electric motor is first shifted without power. If the decoupler that is assigned to the other input shaft is engaged, it is disengaged. Then the clutch of the target gear is synchronized using the electric motor and subsequently engaged. Then the clutch of the gear under load is controlled without load by means of the electric motor and subsequently disengaged. Finally, the other input shaft is accelerated or decelerated, using the electric motor, to the synchronous rotational speed of the other assigned decoupler, and then finally, the decoupler in question is engaged. After the shifting operation, the electric motor can be shifted without power or put into generator operation.
In this way, the shifting operations take place without interruption of traction, but are relatively elaborate and time-consuming. Due to the external synchronization by the electric motor, the clutches can be designed as unsynchronized claw couplings. However, because of the two decouplers, the input constants, the axially parallel arrangement of the electric motor and the axially adjacent arrangement of the gearwheel sets, the constructional complexity and construction space requirements of this known hybrid drive train are unfavorable.